The present invention relates to an appliance for straightening and orienting the roots of selected teeth by the application of controlled force moments to their crowns, hence producing a pivoting action.
Many orthodontic treatment techniques in use today move teeth in a two phase procedure. In the initial phase the forces which are applied to the crowns of the teeth produce a greater displacement of the crown than of the root resulting in a tipping movement.
The latter phase employs moments of force which are also applied to the crowns of the teeth in order to upright the roots, thereby placing them in a position of proper axial inclination, commensurate with normal function, favorable esthetics, and stability. This is termed the torquing phase.
Lingual root torque is difficult to achieve particularly on the maxillary anterior teeth. The reason is that all forces must be applied to the crown, while the center of resistance to root movement is located in a remote position along the apical portion of the root surface. This results in a situation of severe mechanical disadvantage.
Several orthodontic appliances are known to provide root torquing. They generally consist of three basic elements: 1) metal bands which circumferentially encompass the crown of each tooth and are attached to them by cementation; 2) brackets of varying configurations (according to technique) which are affixed to the metal bands; and 3) base arch wire -- usually of a U-shaped configuration which fit through slots in each of the brackets. The base arch wire is generally round or rectangular in cross-section. In some applications brackets may be attached directly to the tooth surface, without using bands, by means of bonding.
The arch wire may act in an active or passive capacity. In the passive mode it acts as a track along which the teeth are moved. In the active mode deformations are incorporated in the base arch wire during its fabrication. When the arch wire is placed into position within the bracket slots these deformations serve to produce forces and moments which move teeth during orthodontic treatment.
One of the early attempts to produce torquing moments consisted of placing a rectangular arch wire, at an angle, within a rectangular slot of a bracket welded to a band. The angular twisting of the stressed arch wire reacted against the bracket and produced a torquing force on the tooth. This method, while it did produce torque, was most disadvantageous, because of the limited degree of flexibility inherent in the arch wire itself. This produced undesirably high magnitudes of force, often resulting in extreme pain and root resorption. Because of inflexibility of the rectangular arch wire, the force became dissipated rapidly, necessitating frequent adjustments of the arch wire at great discomfort to the patient.
Further attempts followed the line of taking the torsional force from the bracket slot and moving it more cervically on the crown closer to the center of resistance to movement. As a result, several varieties of auxiliary torquing appliances capable of being mounted on the arch wire were developed.
In U.S. Pat. No. 3,325,965 issued to Richard J. Muir, there is described an elongated wire formed into a series of contiguous U-shaped loops separated by coils. The intermediate coils between each of the U-shaped loops are wound in an alternating direction and fit loosely around the axis of the base arch wire. The U-shaped loops extend apically when activated, so that they bear against the labial aspect of the anterior teeth. The elongated wire is provided at each of its distal ends with an expanded occlusal loop which extends from the arch wire in a direction opposite to that of the U-shaped loops previously mentioned, and engages against the buccal aspect of the canine and premolar teeth. Thus any potential moments of force coming from the anterior apical loops are produced by a complicated interaction between the arcuate portion of the base arch wire and the Muir Auxiliary which is initially coplanar with the arch wire and is subsequently distorted during activation. During activation conflicting rotary actions of the individual coils are induced because of the non-parallel nature of the planes of rotation of the several sliding coils. Moreover, forces are induced which attempt to rotate these sliding coils within their individual tangent planes to the arch wire. These motions are restrained by the arch wire within which counter reactions are set up. In addition, reactive forces are introduced through contact of the occlusal loops and posterior teeth. This appliance exhibits the following defects:
1. Because of the multiple contiguous loops and coils the wire system is highly flexible and therefore of minimal effectiveness in producing sufficient moments to obtain the required effects.
2. If however, it were conceivable to produce sufficient moments with this mechanism to lingually torque anterior roots, then undesirable buccal root movement of the anchoring canine and premolar teeth may also result through counteraction. The coils in this device serve as a means of attachment to the base arch wire and are not for helical spring action.
3. If one chooses to argue that the auxiliary appliance exhibits helical coil action, then the auxiliary appliance must be considered as being highly inefficient, since the alternating manner in which the coils are wound result in only every other loop closing in one direction. The intermediate loops open in the same direction, consequently producing an appliance in which only alternate loops may possibly provide torquing movement.
4. The arrangement in this appliance results in excessive expansion of the buccal segments of the base arch wire.
5. The device provides an asymmetric loop system with respect to any individual tooth or group of teeth.
Another attempt, known as the Ford Torquing appliance, is similar to that of Muir in that two apical loops are freely mounted on an arch wire. The apical loops are interconnected by windings about the arch wire. The windings have a bridging portion which is engaged by a small finger-like prong soldered to the arch wire. By rotating the apical loops about the arch wire, the engaging prong becomes torsionally loaded causing a reactive force through the windings upon the apical loops. A significant disadvantage of this configuration is the decreased effectiveness of the spring action on each apical loop, since loading occurs only at the prong region activating only the mesial legs of each loop. This also produces an undesirable asymmetry with respect to each tooth.
Recently, a torsion appliance, known as the Warren Torquing Spring, manufactured by the Rocky Mountain Dental Products Company has come into use. This appliance comprises individual U-shaped torquing springs having each leg terminating in an elliptical coil which is adapted to a sliding fit over a rectangular cross-sectional arch wire. Once placed upon the arch wire all the elliptical turns serve as a rigid anchor, binding the appliance to the arch wire.
Because of the rigid attachment of the elliptical coils to the arch wire at the base of the loop the only spring action is that of a simple cantilever beam provided by the legs of the loop. This construction requires an excessive deflection of the loop by as much as 90.degree.. This leads to permanent deformation of the spring due to lost elasticity. Thus severely diminishing the effectiveness of the appliance.
In these respects the Warren Appliance is no different than the conventional Debnam Torquing Arch manufactured by the Rocky Mountain Dental Products Company wherein two finger-like projections are centrally soldered to the base arch wire forming a cantilevered beam. Debnam's appliance exhibits the same inherent defects in design as the Ford Torquing Arch in that spring action is exerted on only one side of the tooth hence producing an asymmetric force system.
The Kitchton auxiliary torquing device manufactured by T.P. Laboratories, La Porte, Ind., consists of two legs extending from a central coil formed in the plane of the legs. The legs which are initially bent have hooked ends. The coil is anchored on the arch wire and the leg ends are carried down and hooked over the base arch wire. This configuration now forms a pair of apical loops. The orientation of the coil is 90.degree. rotated with respect to any of the previously described coils lying in a plane parallel to the labial face of the maxillary central incisor teeth when activated. The coil serves only as a means of attachment to the base arch wire. Attachment may be achieved by the separation and straddling of the coils over the base arch wire in conjunction with a steel ligature tie through the coil center and around the arch wire. Alternately the coil may simply be placed behind and against the base arch wire and then tied to it by ligation. The coil is located on that portion of arch wire between the central incisor teeth.
In either case the holding action is simply a frictional one and slipping may occur. The coil serves merely to aid in the mode of attachment and doesn't function as a source of spring force against the teeth. Any associated spring action which might occur stems from the interaction of the curved arch wire with the planar apical loop configuration, resulting in undesirable expansive counter forces on the base arch wire.
A similar functioning device is Garcia Torquing Auxiliary manufactured by the Unitek Corporation, of California, which utilizes the same holding principle of friction attachments to the base arch wire. However, it utilizes a hook instead of a coil in its central portion.
It is the object of the present invention to provide an improved orthodontic torquing device overcoming the disadvantages found in the prior art appliances.
It is a further object of the present invention to provide an orthodontic torquing device having an improved spring rate and a continual spring action throughout its use in treatment.
It is an object of the present invention to provide an orthodontic torquing appliance which is of simple and convenient manufacture and which may be utilized with numerous conventional types of orthodontic appliances.
The foregoing objects, other objects, as well as numerous advantages of the present invention will be obvious from the following disclosure.